kconfig: Hide the DesignWare SPI driver on unsupported platforms

When users are configuring applications they are given the option
to enable the DesignWare SPI driver. But they should not be given this
option on SoCs that don't have the DesignWare SPI HW.

This commit hides the driver by default by introducing the config
option HAS_SPI_DW.

Fixes: #10825

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>